The present invention relates to a method for manufacturing ink follower, which follows water-base ink filled in an ink reservoir of a ballpoint pen.
The ink for a water-base ballpoint pen has a viscosity of as low as 50 mPa sec to 3 Pa sec, while the ink for an oil-base ballpoint pen, though it has a similar structure to a water-base one, has a viscosity of 3 to 20 Pa sec. Consequently, the ink filled in a water-base ballpoint pen may leak out when the pen is left upward or sideways. Moreover, even a small impact made on the pen may cause its ink to scatter and to stain the hand or the clothes.
There have been conventional arts for a water-base ballpoint pen with its ink in its ink reservoir that it is equipped with an ink follower composed of a gelled material, or a mixture of the gelled material and solid material.
The aims of the arts are to make the ink follower follow the ink smoothly, to make the pen endure the impact when dropped, to prevent the ink from back flow, to give the pen a good appearance, and so on.
A common feature of such arts is that the ink follower, which has pseudo-plasticity, is made from hardly-volatile or non-volatile solvent which is supplemented with some kind of thickener in order that the ink follower may not flow backward when the pen is left sideways or upward.
Moreover, conventional ink follower for water-base ballpoint pens often has very low viscosity and tenacity, as compared with that for conventional oil-base ballpoint pens, which often has equal viscosity to common grease used for lubricant. That is because of making the following property to the ink better.
Amount of the ink of a ballpoint pen necessary for writing varies depending upon the diameter of the ball. In an oil-base ballpoint pen for fine (0.5 mm) to bold (1.0 mm) letters, the amount is 10-30 mg per 100 m. On the other hand, in a water-base ballpoint pen for fine (0.3 mm) to bold (0.7 mm) letters, the amount is 50-300 mg per 100 m. Since the amount of the ink consumed for a water-base ballpoint pen is more than five- to ten-fold of that for an oil-base ballpoint pen, severe ink-following properties are requested for the ink follower for a water-base ballpoint pen. Thus the follower having low viscosity and tenacity has been used as compared with that for an oil-base ballpoint pen.
Lubricant grease with low viscosity and consistency generally has such low stability that oily matter likely separates when left to stand. In addition, if the thickener component in the lubricant grease is likely to move, it causes the grease to lose homogeneity easily by forming a mixture of coarse and dense portions. The lower the viscosity of the thickener of the grease, the less effectively the thickener is dispersed by a disperser such as a double-roll mill, a triple-roll mill, a kneader or a planetary mixer, any one of which is suitable for substances with high viscosity. The thickener is, however, not so low in viscosity as to be capable of being mixed effectively by a disperser such as a bead mill, a sand mill or a homogenizer, any one of which is suitable for substances with low viscosity. Inefficient dispersion causes not only time-dependent instability but also lot-to-lot instability in viscosity and uniformity.
The ink follower for the water-base ballpoint pens consists of materials similar to the lubricant grease, and exhibits time-dependent behaviors based on similar physical laws.
Once the oil is separated due to a time-dependent change, it affects the surfactant in the ink. It weakens the effect of the ink in the surfactant and blocks the ink passage as oil droplets resulting in a bad influence on writing.
Moreover, if the thickener component in the ink follower lacks homogeneity, the ink follower is separated into a portion following the ink and portions adhering to the inner wall of the ink reservoir. The adhering portions not only give the pen an unpleasant appearance, but also mean a corresponding loss of the ink follower, resulting eventually in its failure to perform its function of, for example, preventing the ink from volatilizing or from leaking.
The objects of this invention are to dissolve the defect that conventional ink follower for a water-base ballpoint pen has lot-to-lot and time-dependent instability of quality, and to provide a method for manufacturing the ink follower which has a better following property than the conventional ink follower for water-base ballpoint pens.
As a result of our diligent study of above problems, we have found that, reduced viscosity and surface tension of the base oil under elevated temperature make it easy for particulate thickener such as silica, alumina and titanium oxide and clay thickener to disperse. We have also found that thickener, when homogenized very highly microscopically, always shows its best performance and that it produces increased time-dependent stability and reduced lot-to-lot difference. Thus we have completed our present invention.
Lubricant grease and ink follower for a water-base ballpoint pen are prepared from similar materials by similar processes, but are clearly different from each other from a technical standpoint.
The lubricant grease is usually used only for lubricating, and is, therefore, made to have high structural viscosity and yield value lest the oily constituent of the grease drip from a point where the grease is applied. On the other hand, the ink follower for a water-base ballpoint pen is held in a reservoir with no opening except its rear end, and is used in an environment in which there is no sliding matter except itself. Therefore, the structural viscosity and yield value of the ink follower may be low. It would rather be correct to say that it is necessary for the ink follower to be low in structural viscosity and yield value in order to follow the ink smoothly.
Fine particulate powder such as inorganic thickener (particulate silica, alumina or titanium dioxide), inorganic or organic pigment and fine resin particulate, which gains structural viscosity in liquid, generally shows a lower thickening effect and a lower yield value when it is well-dispersed.
The solvent used for the base oil for the ink follower is selected from polybutenes, liquid paraffin, highly purified mineral oil such as spindle oil, silicone oil such as dimethyl polysiloxane and methyl phenyl polysiloxane and so on. They do not dissolve in a water-base ink, and has only a small volatile loss. They generally have a better wetting property with resins such as polypropylene, polyethylene and so on, used for an ink reservoir than that of water-base ink. Thus the consumption of the ink is easy to recognize.
Polybutenes and silicone oils, though some kinds of them are highly volatile, can withstand for two years or more at room temperature if their volatile loss is not more than about 0.2% by weight under a JIS C-2320 method at 98xc2x0 C. for five hours.
The volatility of polybutenes largely depends upon their molecular weight. Polybutenes with average molecular weight more than about 500 may satisfy the above volatile loss.
Since the volatile loss of silicone oils also depends upon their molecular structure, it cannot be determined only by their molecular weight. Therefore, the volatile loss of silicone oils is recommended to be measured practically by the method as described above.
Aerozyl R-972, R-974D, R-976D and RY-200 (trade names, Nippon Aerozyl) are preferable material for the thickener for the present invention. They may be used either solely or jointly and the total additional amount to the total amount of the ink follower is 1-10% by weight.
Although pseudo-plasticity can be given even when the amount is less than 1%, quantitative lack of the thickener is evident and separation of oil cannot be prevented. In addition, even if viscosity is increased using particulate silica, titanium oxide or aluminum as well as other powder such as inorganic and organic pigment whose BET specific surface area is around 50 m2/cm, to which pseudo-plasticity is most unlikely given, the pseudo-plasticity and the yield value at the amount more than 10% become so strong that the following property to ink becomes bad.
A more preferable range is 2-6% by weight to the total amount of the ink follower. Within such a range of additional amount, it is possible to prevent the oil separation and also to ensure a good following property to ink.
Hydrophilic thickener, such as Aerozyl #200, 380, 300, 100 and OX50 (Nippon Aerozyl Co., Ltd.), particulate alumina and ultra-particulate titanium dioxide, both of which are manufactured by a gaseous phase method of the same company, and the mixture of these materials can be prevented from interfering with the ink when the ink follower contains the substances such as surfactant, silane coupling agent, fluorocarbon, and methylhydrogen silicone, each of which has a hydrophilic-lipophilic balance (HLB) value of less than 4, preferably of less than 2. When silicone oil is used the for base oil of the ink follower, it is often possible for the ink follower, without adding other substance, to avoid interfering with the ink.
It is effective to use additive such as surfactant to the ink follower in order to improve its property of following the ink.
Even irrespective of the kind of surfactant, it is not preferable to use the surfactant that dissolves in the ink during storage, but preferable to use nonionic surfactant with an HLB value less than 4. Moreover, the so-called fluorine-surfactant and silicone-surfactant are the most preferable additives since they can drastically lower the surface tension of the base oil.
It is also preferable for the object of this invention to add above-mentioned silane coupling agent, methylhydrogen silicone, etc. since they are effective for stabilization of the dispersion of the thickener, homogenization and hydrophobization. It is very preferable to use additives unless it makes an ill effect for the stability of the ink follower and for the quality of the ink.
The amount of these additives to be used is generally from 0.01%, which is minimal effective concentration, to about 5% by weight. The amount over 5% by weight does not produce any better result, though it may not present any problem in quality.
More preferred range is 0.1-1% by weight. Surfactant acts on the xe2x80x9csurfacexe2x80x9d as its name shows and, therefore, the effect does not increase even if it is added too excessively. Rather, even when surfactant having very strong hydrophobicity is used, there are components having lipophilic groups in the ink and a bad influence may be resulted in view of a property of the pen as a whole. Therefore, too much use is not recommended in terms of stability with a lapse of time. According to the experiences of the present inventors, even in the case of a surfactant having an excellent characteristic property when used as base oil such as polyether-modified silicone, there was no change in terms of property when its amount was more than 1%. In addition, there are some cases where the effect of surfactant becomes weak time-dependently due to decomposition or the like. When such cases are taken into consideration, it is questionable to make its amount to a minimum extent even if that is effective. From our experiences, there was no case where the effect of the surfactant was lost time-dependently when 0.1% or more was added.
Since the present invention includes a method for manufacturing, it will be illustrated in detail by way of Examples. Conceptionally, it is characterized in that the temperature is made higher than ambient temperature in a part of or most of the manufacturing processes whereby base oil and thickener are made compatible.
The temperature applied in the present invention is any temperature between 40xc2x0 C. and 130xc2x0 C.
It is quite rare in Japan that, even in the midsummer, ambient temperature exceeds 40xc2x0 C. Even when the ambieat temperature becomes greatly higher than 40xc2x0 C., it is still rare throughout the year that the temperature of the materials placed in a room becomes 40xc2x0 C. or higher. Thus, application of the temperature of 40xc2x0 C. or higher intentionally means the seasonal variation of the temperature during the manufacture is absorbed and, at the temperature lower than, 40xc2x0 C., the seasonal variation is unable to be absorbed unless intentional refrigeration is conducted. Although such intentional refrigeration contributes to a reduction in lot-to-lot difference, which is one of the objects of the present invention, that is contrary to the main object of the present invention that thickener is apt to be dispersed homogeneously by means of heating.
Temperature of 130xc2x0 C. means an upper limit of common steam heating. There are many heating methods such as electric heating and a direct fire and, although the heating method itself is out of question in the present invention, we have concluded that steam heating is the safest and simplest method.
Homogenization of ink follower was not affected even if heating was done at 130xc2x0 C. or higher. Rather, there were many cases where the low molecular components of the base oil or, in other words, the parts which were apt to be volatile were evaporated whereby the dispersion in the components for each lot of the base oil is apt to reflect the dispersion in the quality of the ink follower. In addition, some of additives such as surfactant are denatured at around 100xc2x0 C. although that may vary depending upon the heating time and, accordingly, excessive heating is not preferred.
Under an atmosphere of ordinary pressure, more preferred temperature range intended in the present invention is from 100xc2x0 C. to 130xc2x0 C. when thickener in fine particles is used while, when clay thickener is used, heating at not higher than 60xc2x0 C. or non-heating is preferred before the dispersing step such as by a triple-roll mill because of the use of a low molecular alcohol for swelling the clay thickener. After that, the temperature may be from 60xc2x0 C. to 130xc2x0 C.
Powder of inorganic particulates and clay thickener as well as other materials absorb moisture,in air during storage but, since the moisture can be removed by heating at 100xc2x0 C. or higher, quality is more stabilized when a step of 100xc2x0 C. or higher is included.
Low molecular alcohol with a carbon number about one to four is used as auxiliary agent in the case of clay thickener. Although this auxiliary agent is evaporated and removed finally, it should be present until the step where the shearing force is applied mostly strongly and the total system is to be kept at 60xc2x0 C. or lower.
When the auxiliary agent is completely evaporated, heating at 100xc2x0 C. or higher is preferred for excluding the moisture in the material but, if the auxiliary agent remains, it is preferred that the auxiliary agent is gradually evaporated at around 60xc2x0 C.-80xc2x0 C.
When a rapid heating is carried out, the auxiliary agent is boiled whereby the dispersed system which is expressly homogenized may be damaged.
The above-mentioned temperature range is not preferred when the ink follower is subjected to a debubbling treatment in a reduced atmosphere. This is because low molecular components and additives in the base oil are evaporated therefrom.
The temperature may also vary depending upon the degree of vacuation and is preferably 60xc2x0 C. or lower when vacuated to an extent of about 0.1 atm (10 kPa) or lower.
The essential object of the present(invention is that viscosity and surface tension of the base oil are reduced by raising the temperature whereby thickener and base oil are made compatible. Accordingly, it is preferred to heat at 60xc2x0 C. or higher even in the process for manufacturing ink follower including a vacuating step. Even in such a case, however, it is still preferred to cool at 60xc2x0 C. or lower followed by vacuating.
Another example where application of temperature is effective is a step for diluting the concentrated dispersion.
In a method for a homogeneous dispersing of the powder of inorganic particulates and the clay thickener, a disperser for high viscosity such as a double-roll mill, a triple-roll miller, a kneader and a planetary mixer is used. In such a machine, substance of higher viscosity is more efficiently dispersed. Therefore, there may be the cases where all of the substrate components are not added initially but the components are dispersed in high concentrations, or where only highly viscous components in the base oil components are dispersed and then the residual base oil components are added thereto to dilute.
In such cases, activity of the base oil components is higher and a more homogeneous mixing is resulted when the temperature of the base oil components which are added later is raised to 40xc2x0 C. or higher and then added. It is still better that the addition is not conducted at a time but is done for several times little by little with stirring whereby a homogeneous state is resulted within shorter time as a result.
An example for a method of filling the ink follower of the present invention is that the ink is filled in an ink reservoir, a pen point is attached and then ink follower is charged. After that, a strong centrifugal force is applied by means of a centrifugal separator in the direction of from the tail end to the pen point whereby the ink follower is filled with a good appearance containing no air or the like between the ink and the ink follower.